For example, on the occasion of forming an element region on a semiconductor substrate, a lot of pn junctions are used. In addition, such a SOI (silicon on insulator) substrate that a silicon thin film is formed on a substrate surface through an insulating film is widely used for various semiconductor devices such as DRAM. In addition, such a glass substrate that a semiconductor thin film is formed on a substrate surface attracts attention with planning for miniaturization and realization of high speed of a liquid crystal panel by integrating a liquid crystal drive circuit including thin film transistors (TFTs) in this semiconductor thin film.
On the occasion of forming various semiconductor devices in this manner, pn junctions are used. As the suchlike method of forming pn junctions, a method of introducing p type impurities such as boron by ion implantation into a n type silicon substrate and thereafter, electrically activating them by a halogen lamp, is used conventionally.
For example, as a method of introducing boron which is a p type impurity, plasma doping is expected as a next generation method which can introduce particles effectively with very low energy, in addition to ion implantation.
As a method of electrically activating introduced ions such as boron ions, a method of irradiating xenon flash lamp light, all solid-state laser light, and excimer laser right, other than halogen lamp light, and the like have been researched and developed.
Here, a method of forming a shallow activated layer by utilizing a difference of optical absorption coefficients of silicon crystal and amorphous silicon has been proposed. In sum, an optical absorption coefficient of amorphous silicon is larger as compared with that of silicon crystal, in a wavelength range of 375 nm or more. Then, for example, an amorphous layer is formed in advance on a silicon substrate surface prior to irradiating light, and after that, light is irradiated, and thereby, a lot of light energy is let absorbed by the amorphous layer, to form a shallow activated layer. In these reports, it is general that realization of pre-amorphous of a substrate surface is carried out, prior to introduction of impurities, and after that, impurities are introduced. Ion implantation of germanium and silicon is used for the realization of pre-amorphous (see, Non-Patent Documents 1, 2, 3, 4, 5 and Patent Document 1).
In recent days, such a process that changing a silicon very shallow layer to amorphous by use of plasma, and plasma doping were combined, has been proposed by inventors of this case. According to this, plasma such as helium is irradiated to a silicon substrate by use of a plasma irradiation apparatus, and thereby, amorphous of a very shallow layer on a silicon surface can be realized. Further, plasma doping is carried out by plasma of gas including boron through the use of the same apparatus, and thereby, very low impurity introduction can be carried out. In this method, low energy plasma is used, and therefore, there is such an advantage that it is possible to realize amorphous of a very low region effectively, as compared with ion implantation. Further, by using it with plasma doping at the same time, it is possible to easily form a very low impurity layer which is changed to amorphous, by 1 unit of the apparatus.
Non-Patent Document 1: Ext. Abstr. Of IWJT, pp23-26, Tokyo, 2002.
Non-Patent Document 2: Symposium on VLSI Technology Digest of Technical Papers, pp 53-54, Kyoto, 2003.
Non-Patent Document 3: Ext. Abstr. Of IWJT, pp31-34, Tokyo, 2002.
Non-Patent Document 4: Ext. Abstr. Of IWJT, pp27-28, Tokyo, 2002.
Non-Patent Document 5: 2000 International Conference on Ion Implantation Technology Proceedings, 2000, pp.175-177.
Patent Document 1: U.S. Pat. No. 3,054,123 (P3054123)